1. Field of the Invention
The present invention relates to a high heat-resistant catalyst support which is used in an exhaust-gas-purifying catalyst, a catalyst which uses the catalyst support, and a process for producing the same.
2. Description of the Related Art
For instance, Japanese Unexamined Patent Publication (KOKAI) No. 7-075,735 discloses a catalyst support. The catalyst support is composed of amorphous alumina as a major component, and contains an NO.sub.x storage element which is composed of an alkali metal, an alkaline-earth metal or a rare-earth element. According to the publication, in the support, the alumina and the NO.sub.x storage element do not form stable compounds in a temperature range where the amorphous alumina does not crystallize. Consequently, the catalyst support is inhibited from exhibiting a decreased NO.sub.x storage ability. Further, since the NO.sub.x storage element can be mixed in the amorphous alumina in a highly dispersed manner, the sulfates are less likely to grow granularly even when the NO.sub.x storage element reacts with sulfuric oxides to produce the sulfates. Thus, the decrease in the NO.sub.x storage ability (i.e., the sulfur poisoning), which is caused by the granular growth of the sulfates, is less likely to occur. Furthermore, since the generated sulfates are very fine, they are likely to be reduced in a reducing atmosphere. Hence, the catalyst support has an advantage in that the NO.sub.x storage ability of the NO.sub.x storage element can be recovered.
The aforementioned catalyst support is produced by a sol-gel method in which an alkoxide is used as a raw material. However, since the alkoxide is expensive, the resulting catalyst support is expensive as well. Further, since the support powder, which is prepared by the sol-gel method, is constituted by fine particles, there might arise a possibility that the catalyst support exhibits a reduced specific surface area by granular growth when it is used at elevated temperatures exceeding 1,000.degree. C.